Thermal atomic layer deposition of ternary gallium oxide thin films

ABSTRACT

The present disclosure describes a method of a thermal atomic layer deposition (ALD) process of depositing a ternary gallium oxide thin film, which includes gallium, a metal element other than gallium, and oxygen. The disclosed method starts with providing a reactive surface. Next, one or more ALD growth cycles are conducted. Each ALD growth cycle includes one or more first ALD sub-cycles and one or more second ALD sub-cycles. Herein, conducting each first ALD sub-cycles includes applying a pulse of a first metal precursor and a pulse of water sequentially, where the first metal precursor is a gallium compound. Conducting each second ALD sub-cycles includes applying a pulse of a second metal precursor and a pulse of water sequentially, where the second metal precursor includes the metal element other than gallium.

GOVERNMENT SUPPORT

This invention was made with government funds under Agreement No.HR0011-18-3-0004 awarded by The Defense Advanced Research ProjectsAgency (DARPA). The U.S. Government has certain rights in thisinvention.

FIELD OF THE DISCLOSURE

The technology of the disclosure relates to growth of ternary galliumoxide thin films, which include gallium, another metal element, andoxygen, by thermal atomic layer deposition (ALD) under conditionscompatible with back-end-of-line (BEOL) processing.

BACKGROUND

With the rapid development of semiconductor technologies, metal oxidematerials are widely used in forming dielectric layers in semiconductordevices. Compared to binary metal oxide materials (formed from one metalcomponent with oxygen), ternary metal oxide materials (formed from twometal components with oxygen) have been relatively underdeveloped, thusthe ternary metal oxide materials may have more potential for highimpact materials. In addition, the ternary metal oxide materials mayprovide further flexibility in band gap, carrier mobility, and/orthermal conductivity. Some of these ternary metal oxide materials, suchas ternary gallium oxides, which include gallium, another metal element,and oxygen, have been shown to have desirable potential in nextgeneration thin film applications including integrated circuit design tophotovoltaic devices.

Contemporary thin film fabrication uses a variety of techniques such assol-gel method, spray pyrolysis, spin coating, electron-beamplasma-deposition, sputtering, and chemical vapor deposition (CVD)including plasma-enhanced CVD (PECVD) and atomic layer deposition (ALD).Among them, due to the layer-by-layer growth, ALD is one of the mostpromising techniques for growing thin films with atomic level precision.

The development of ternary oxide ALD has been outpaced by thedevelopment of binary ALD processes. This is because it is difficult todesign precursors that deposit high purity films with tightly controlledreaction chemistry. In particular, it is difficult to control theelemental ratio of a resulting ternary film.

Accordingly, there is an object of the present disclosure to provide animproved ALD process for depositing ternary metal oxide thin films,especially ternary gallium oxide thin films, without sacrificingimpurity requirements. In addition, the improved ALD process is capableof controlling the concentration ratio of gallium versus the other metalin the resulting thin films.

SUMMARY

The present disclosure describes an exemplary method of a thermal atomiclayer deposition (ALD) process of depositing a ternary gallium oxidethin film, which includes gallium, another metal element, and oxygen.The disclosed method starts with providing a reactive surface. Then oneor more ALD growth cycles, each of which includes one or more first ALDsub-cycles and one or more second ALD sub-cycles, are conducted. Herein,conducting each of the one or more first ALD sub-cycles includesapplying a pulse of a first metal precursor and applying a pulse of anoxygen source after applying the pulse of the first metal precursor. Thefirst metal precursor is a gallium compound with one or more of an alkylligand, an amido ligand, an amidinato ligand, an alkenyl ligand, and aguanidinato ligand. Conducting each of the one or more second ALDsub-cycles includes applying a pulse of a second metal precursor andapplying a pulse of an oxygen source after applying the pulse of thesecond metal precursor. The second metal precursor includes the metalelement other than gallium.

In one embodiment of the exemplary method, the oxygen source in each ofthe one or more first ALD sub-cycles is water, and the oxygen source ineach of the one or more second ALD sub-cycles is water.

According to one embodiment, the exemplary method further includesrepeating the ALD growth cycle.

In one embodiment of the exemplary method, conducting each of the one ormore ALD growth cycles comprises conducting one first ALD sub-cycle andconducting one second ALD sub-cycle in series.

In one embodiment of the exemplary method, the first ALD sub-cycle isconducted before the second ALD sub-cycle within one ALD growth cycle.

In one embodiment of the exemplary method, the first ALD sub-cycle isconducted after the second ALD sub-cycle within one ALD growth cycle.

In one embodiment of the exemplary method, conducting each of the one ormore ALD growth cycles comprises conducting one first ALD sub-cycle andconducting two sequential second ALD sub-cycles.

In one embodiment of the exemplary method, the first ALD sub-cycle isfollowed by the two sequential second ALD sub-cycles within one ALDgrowth cycle.

In one embodiment of the exemplary method, conducting each of the one ormore first ALD sub-cycles further includes one purge step betweenapplying the pulse of the first metal precursor and applying the pulseof water, and another purge step after applying the pulse of water.

In one embodiment of the exemplary method, conducting each of the one ormore second ALD sub-cycles further comprises one purge step betweenapplying the pulse of the second metal precursor and applying the pulseof water, and another purge step after applying the pulse of water.

In one embodiment of the exemplary method, the first metal precursor hasa formula of GaL1(L2)₂. Herein, Ga is a central gallium atom, and L1 andL2 are ligands surrounding the central gallium atom. Each of L1 and L2is an alkyl ligand, an amido ligand, an amidinato ligand, an alkenylligand, or a guanidinato ligand.

In one embodiment of the exemplary method, L1 and L2 are a same ligand.

In one embodiment of the exemplary method, L1 and L2 are differentligands.

In one embodiment of the exemplary method, each of L1 and L2 is selectedfrom one of a N,N′-diisopropylacetamidinato-group (-amd), aN,N′-diisopropylformamidinato-group (-famd), a methyl group (-Me), aN-butyl group (-nBu), a vinyl group (-vinyl), a dimethylamido-group(-NMe₂), and a N,N′-diisopropyl-N-dimethyl-guanidinato-group (-guan).

In one embodiment of the exemplary method, the first metal precursor isone of a group consisting of Ga(amd)₃, [Ga(famd)₃]₂, Ga(amd)₂(Me),Ga(amd)(Me)₂, Ga(amd)(nBu)₂, Ga(amd)(vinyl)₂, Ga(amd)(NMe₂)₂,Ga(guan)(NMe₂)₂, and [Ga(NMe₂)₃]₂.

In one embodiment of the exemplary method, the second metal precursor isan organic aluminum precursor.

In one embodiment of the exemplary method, the first metal precursor isGa(amd)₃, the second metal precursor is Trimethylaluminium (TMA), andthe ternary metal oxide thin film is formed of gallium aluminum oxide(GaxAl1-x)₂O₃, wherein 0<x<1.

In one embodiment of the exemplary method, a concentration ratio ofgallium versus the metal element in the resulting ternary gallium oxidethin film from the thermal ALD process is dependent on a pulse ratiobetween pulses of the first metal precursor and pulses of the secondmetal precursor within one ALD growth cycle.

In one embodiment of the exemplary method, the concentration ratio ofgallium versus the metal element in the resulting ternary gallium oxidethin film is further dependent on sub-cycle order in one ALD growthcycle, pulsing time of each pulse of the first metal precursor, andpulsing time of each pulse of the second metal precursor.

In one embodiment of the exemplary method, in one ALD growth cycle, anumber of the pulses of the first metal precursor is N, and a number ofthe pulses of the second metal precursor is M, wherein N and M arepositive integers.

In another aspect, any of the foregoing aspects individually ortogether, and/or various separate aspects and features as describedherein, may be combined for additional advantage. Any of the variousfeatures and elements as disclosed herein may be combined with one ormore other disclosed features and elements unless indicated to thecontrary herein.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 shows an exemplary atomic layer deposition (ALD) cycle in a ALDprocess for growing a binary metal oxide film.

FIGS. 2A and 2B provide exemplary gallium precursors used to form aternary gallium oxide thin film in a thermal ALD process according toone embodiment of the present disclosure.

FIG. 3 provides an evaporation chart of some exemplary galliumprecursors shown in FIG. 2A.

FIGS. 4A and 4B provide experimental results of binary gallium oxidefilm growth in a thermal ALD process by using Ga(amd)₃ as a galliumprecursor.

FIG. 5 provides an exemplary flow chart of a thermal ALD process forgrowth of a ternary gallium oxide film according to one embodiment ofthe present disclosure.

FIG. 6 provides an exemplary ternary gallium oxide thin film formed overa substrate by the thermal ALD process illustrated in FIG. 5 .

FIGS. 7A and 7B provide experimental results of the ternary galliumoxide film growth in the thermal ALD process illustrated in FIG. 5 .

It will be understood that for clear illustrations, FIGS. 1-7B may notbe drawn to scale.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element such as a layer, region, orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present.Likewise, it will be understood that when an element such as a layer,region, or substrate is referred to as being “over” or extending “over”another element, it can be directly over or extend directly over theother element or intervening elements may also be present. In contrast,when an element is referred to as being “directly over” or extending“directly over” another element, there are no intervening elementspresent. It will also be understood that when an element is referred toas being “connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer, or region to another element, layer, or region asillustrated in the Figures. It will be understood that these terms andthose discussed above are intended to encompass different orientationsof the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including” when used herein specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

Embodiments are described herein with reference to schematicillustrations of embodiments of the disclosure. As such, the actualdimensions of the layers and elements can be different, and variationsfrom the shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are expected. For example, aregion illustrated or described as square or rectangular can haverounded or curved features, and regions shown as straight lines may havesome irregularity. Thus, the regions illustrated in the figures areschematic and their shapes are not intended to illustrate the preciseshape of a region of a device and are not intended to limit the scope ofthe disclosure. Additionally, sizes of structures or regions may beexaggerated relative to other structures or regions for illustrativepurposes and, thus, are provided to illustrate the general structures ofthe present subject matter and may or may not be drawn to scale. Commonelements between figures may be shown herein with common element numbersand may not be subsequently re-described.

The present disclosure describes a thermal atomic layer deposition (ALD)process of depositing a ternary gallium oxide thin film (i.e., a dopedgallium oxide thin film), which includes gallium, another metal element,and oxygen. The thermal ALD process is a subset of CVD and has beenknown for its excellent film thickness controllability as well asresulting pin-hole free films of high density.

The thermal ALD process is driven by surface reactivities ofvolatile/vapor precursors, which are applied as a series of sequential,non-overlapping pulses to form one atomic layer at a time. For each ofthese pulses, one volatile/vapor precursor reacts with reactive specieson a current surface in a self-limiting way, and once all the reactivespecies on the current surface are consumed, the reaction is terminatedand new surface species are yielded. By utilizing differentvolatile/vapor precursors and/or by applying different pulses of thevolatile/vapor precursors, the film thickness can be controlled in thethermal ALD process. For instance, the more times the volatile/vaporprecursors are pulsed in the thermal ALD process, the thicker the filmmay be formed.

FIG. 1 shows an exemplary ALD cycle in a typical ALD process. Herein,the ALD cycle starts with a surface with hydroxyls (only three hydroxylsare shown for simplicity) as the reactive species. A pulse of avaporized metal precursor ML₃ (e.g., Trimethylaluminium, M is aluminumand L is a methyl ligand) is firstly applied to the surface. The vapormetal precursor ML₃ reacts with the surface (first reaction), such thata proton (e.g. hydrogen proton, H) is transferred to the ligand and aO—M bond is formed. The resulting protonated ligand (e.g., HL) should bevolatile and unreactive, which will allow it to be purged from thesystem. Notice that once each hydrogen proton of the surface hydroxylsis replaced (i.e., each reactive species is consumed), the reaction ofthe vapor metal precursor with the surface will be terminated.

Next, water is introduced as a reactant and reacts with the M-L from thevapor metal precursor (second reaction). As such, each ligand (-L) isreplaced by one hydroxyl (—OH) in water, and hydrogen protons of waterand the ligands are combined to generate more by-product HL. Notice thatonce each ligand (-L) is replaced, the reaction between water and theM-L from the vapor metal precursor will be terminated. Herein, O-M-Obecomes part of the growing film and M-OH presents a new hydroxyl coatedsurface that is ready for the ALD cycle to start all over again.

It is clear that the metal precursor(s) is a key factor in the ALDprocess. The volatility, thermal stability, and reactivity of a metalprecursor used in the ALD process will significantly affect the qualityand thickness of the final film. Typically, the metal precursor(s) usedin the thermal ALD process must avoid condensing on the surface (i.e.,volatile) in a certain temperature/pressure window, must avoid thermaldecomposition (i.e., thermal stable) in the certain temperature/pressurewindow, and must react at the surface and with the reactant (i.e.,sufficient reactivity) in the certain temperature/pressure window. Ifthe metal precursor cannot be vaporized or the metal precursor cannotreact at the surface or react with the reactant within the certaintemperature/pressure window, it is not appropriate for the ALD processto operate in such a temperature/pressure window. In addition, it isnecessary to have appropriate metal precursor(s) that can perform cleanreactions (i.e., without side-reactions or impurity incorporation) inthe certain temperature/pressure window.

In one or more embodiments of the present disclosure, the thermal ALDprocess of ternary gallium oxide film is achieved by utilizing a firstmetal (i.e., gallium) precursor, a second metal (other than gallium,e.g. aluminum) precursor, and water (H₂O) Hydrogen peroxide (H₂O₂) at arelatively low temperature, no higher than 400° C. Herein, thefirst/second metal precursor refers to a first/second molecule thatincludes the first/second metal element and one or more types of ligandssurrounding the first/second metal element. The first/second metalprecursor is eligible to vaporize and is thermal stable within aspecific temperature window. In addition, the first/second metalprecursor should undergo self-limiting surface reactivity that producesvolatile by-products, where the by-products will not etch the formedfilm. In the disclosed thermal ALD process of the ternary gallium oxidefilm, water or Hydrogen peroxide is an oxygen source rather than a morereactive reagent, such as ozone or plasmas.

In one embodiment, the first metal precursor is a homoleptic galliumcompound or a heteroleptic gallium compound with a formula GaL1(L2)₂.Herein, Ga is a central gallium atom, and L1 and L2 are ligandssurrounding the central gallium atom. L1 and L2 each may be an alkylligand, an amido ligand, an amidinato ligand, an alkenyl ligand, or aguanidinato ligand. In different cases, L1 and L2 may be a same ordifferent ligand, and may be chosen from aN,N′-diisopropylacetamidinato-group (-amd), aN,N′-diisopropylformamidinato-group (-famd), a methyl group (-Me), aN-butyl group (-nBu), a vinyl group (-vinyl), a dimethylamido-group(-NMe₂), and a N,N′-diisopropyl-N-dimethyl-guanidinato-group (-guan).For instance, the first metal precursor may be Ga(amd)₃, Ga(amd)₂(Me),Ga(amd)(Me)₂, Ga(amd)(nBu)₂, Ga(amd)(vinyl)₂, Ga(amd)(NMe₂)₂,Ga(guan)(NMe₂)₂, [Ga(famd)₃]₂ or [Ga(NMe₂)₃]₂ as illustrated in FIGS. 2Aand 2B.

FIG. 3 shows a thermogravimetric analysis curve of some of these galliumprecursors at atmospheric pressure: Ga(amd)₃, Ga(amd)₂(Me),Ga(amd)(Me)₂, and Ga(amd)(nBu)₂. Ga(amd)(Me)₂ starts to evaporate atabout 90° C. and substantially fully evaporates at about 140° C.,Ga(amd)₂(Me) starts to evaporate at about 90° C. and substantially fullyevaporates at about 275° C., Ga(amd)(nBu)2 starts to evaporate at about135° C. and substantially fully evaporates at about 225° C., andGa(amd)3 starts to evaporate at about 160° C. and substantially fullyevaporates at about 325° C. It is illustrated herein that each ofGa(amd)₃, Ga(amd)₂(Me), Ga(amd)(Me)₂, and Ga(amd)(nBu)₂ is volatile at acertain temperature range. In addition, each evaporating curve ofGa(amd)₃, Ga(amd)₂(Me), Ga(amd)(Me)₂, and Ga(amd)(nBu)₂ is relativelysmooth. Therefore, Ga(amd)₃, Ga(amd)₂(Me), Ga(amd)(Me)₂, andGa(amd)(nBu)₂ are thermally stable without decomposition in certaintemperature windows.

For different applications, the thermal ALD process may operate atdifferent temperature windows. Based on a temperature window of thethermal ALD process, the first metal precursor could be carefullyselected. In one embodiment, the evaporating starting temperature of thefirst metal precursor may be below or within the temperature window ofthe thermal ALD process, while the fully evaporating temperature of thefirst metal precursor may be above the temperature window of the thermalALD process. Herein, the first metal precursor demonstrates volatilityand thermal stability over a range of temperatures, which satisfiesrequirements for the thermal ALD processing.

FIG. 4A illustrates a quartz crystal microbalance (QCM) observation ofbinary gallium oxide film growth in a thermal ALD process by usingGa(amd)₃ as a metal precursor and water as an oxygen source. FIG. 4Billustrates a vapor delivery pressure chart for both Ga(amd)₃ pulses andwater pulses. The QCM in FIG. 4A shows stepwise growth of the binarygallium oxide film, but the growth steps decrease for each ALD cycle. Inaddition, the vapor delivery pressure chart in FIG. 4B shows decreasingvapor delivery pressure of Ga(amd)₃ pulses for ALD cycles. In otherwords, Ga(amd)₃ is less vaporized for one pulse in each ALD cycle. It isproven that the metal precursor Ga(amd)₃ can be nucleated onto hydroxylsurfaces. However, the metal precursor Ga(amd)₃ does not show sustainedbulk growth of binary gallium oxide film with water. Herein, the binarygallium oxide film may stop growing at about 0.5 Å.

The second metal precursor is therefore introduced to boost precursordelivery and sustain bulk growth of the oxide film. In one embodiment,since the gallium precursor itself tends to nucleate with the aluminumoxide surfaces, the second metal precursor may be an aluminum precursor.For instance, the second metal precursor may be Trimethylaluminium(TMA), and the grown oxide film is a ternary metal oxide film galliumaluminum oxide (GaxAl1-x)₂O₃(0<x<1).

FIG. 5 shows an exemplary flow chart of a thermal ALD process forternary gallium oxide film growth by using the first metal precursor(i.e., gallium precursor), a second metal precursor (e.g., TMA), andwater. Although steps of the flow chart are illustrated in a series,these steps are not necessarily order dependent. Some steps may be donein a different order than that presented.

Further, processes within the scope of this disclosure may include feweror more steps than those illustrated in the flow chart.

Initially, a surface (e.g, a silicon substrate surface) with reactivehydroxyls are provided (Step 402) in a process chamber and under acertain temperature and pressure. A pulse of the gallium precursor isthen delivered (Step 404) into the process chamber, and the vaporizedgallium precursor reacts with the hydroxyls on the surface so as to forma first chemically bound monolayer on the surface. A pulse of water isfollowed (Step 406), and the vaporized water reacts with the firstmonolayer material. As such, a new first hydroxyl (i.e.,gallium-hydroxyl, Ga—OH) coated surface is ready for further deposition.A temperature and pressure for the pulse of the gallium precursor and atemperature and pressure for the pulse of water may need to be carefullyselected to ensure that the gallium precursor can remain thermallystable and the occurring reactions have no/negligible side-reactions andno/negligible impurity incorporation.

One pulse of the gallium precursor and one followed pulse of water forma first ALD sub-cycle. In some applications, the first ALD sub-cycle mayalso include one purge step between the pulse of the gallium precursorand the pulse of water, and another purge step after the pulse of waterto remove the remaining gallium precursor, water, and/or by-product(s)after reactions. The duration of each purge step may be long enough tofully remove the remaining gallium precursor, water, and/orby-product(s) so as to avoid side-reactions.

Next, a pulse of the second metal precursor (e.g., TMA) is deliveredinto the process chamber (Step 408), and the vaporized second metalprecursor reacts with the new first hydroxyls (i.e., Ga—OH) formed fromthe first ALD sub-cycle. Herein, a second chemically bound monolayer isformed due to the second metal precursor. A pulse of water is followed(Step 410), and the vaporized water reacts with the second monolayermaterial. As such, a new second hydroxyl coated (e.g.,aluminum-hydroxyl, Al—OH) surface is ready for further deposition. Atemperature and pressure for the pulse of the second metal precursor anda temperature and pressure for the pulse of water need to be carefullyselected to ensure that the second metal precursor can remain thermallystable and the occurring reactions have no/negligible side-reactions andno/negligible impurity incorporation.

One pulse of the second metal precursor and one followed pulse of waterform a second ALD sub-cycle. In some applications, the second ALDsub-cycle may also include one purge step between the pulse of thesecond metal precursor and the pulse of water, and another purge stepafter the pulse of water to remove the remaining second metal precursor,water, and/or by-product(s) after reactions. The duration of each purgestep should be long enough to fully remove the remaining second metalprecursor, water, and/or by-product(s) so as to avoid side-reactions.

The pulse of the gallium precursor in the first ALD sub-cycle and thepulse of the second metal precursor in the second ALD sub-cycle may havea same or different pulsing duration (i.e., time required to deliver thevaporized precursor). In addition, the temperature, pressure, and/orother conditions in the first ALD sub-cycle may be different orpartially different from those in the second ALD sub-cycle.

In one embodiment, one first ALD sub-cycle and one followed second ALDsub-cycle may form one ALD growth cycle, where such ALD growth cycle maybe repeated a number of different times based on thickness requirementsin different applications. If the second metal precursor is TMA, thegallium precursor will react with the Al-OH surface in the repeatedfirst ALD sub-cycle (except the initial first ALD sub-cycle).

In one embodiment, one first ALD sub-cycle is followed by two second ALDsub-cycles in series to form one ALD growth cycle, where such ALD growthcycle may be repeated a number of different times based on thicknessrequirements in different applications. If the second metal precursor isTMA, the gallium precursor will still react with the Al—OH surface inthe repeated first ALD sub-cycle (except the initial first ALDsub-cycle). Notice that, the concentration ratio of gallium versusaluminum in the resulting thin film from the thermal ALD process isdependent on the pulse ratio of the gallium precursor and the TMAprecursor in one ALD growth cycle.

In one embodiment, the second ALD sub-cycle (instead of the first ALDsub-cycle) is applied at the beginning of the thermal ALD process andfollowed by the first ALD sub-cycle to form one ALD growth cycle, wheresuch ALD growth cycle may be repeated a number of different times basedon thickness requirements in different applications. If the second metalprecursor is TMA, the gallium precursor will always react with the Al—OHsurface (including the initial first ALD sub-cycle).

In general, one ALD growth cycle may include one or more first ALDsub-cycles and one or more second ALD sub-cycles. The one or more firstALD sub-cycles and one or more second ALD sub-cycles may be appliedsequentially in various possible orders. A concentration ratio ofgallium versus the second metal element (e.g., aluminum) in theresulting ternary gallium oxide thin film can be controlled depending onALD processing conditions, such as a sub-cycle ratio (i.e., the pulseratio between the first metal precursor and the second metal precursor)in one ALD growth cycle, sub-cycle order in one ALD growth cycle,pulsing time of first/second metal precursor, and etc. Notice thatvarious pulse ratios of the first metal precursor and the second metalprecursor can be applied within one ALD growth cycle to achievedifferent concentration ratios of gallium versus the second metalelement in the resulting ternary gallium oxide thin film (e.g., notlimited by 1:1 or 1:2 as described above). In other words, in one ALDgrowth cycle, a number of the pulses of the first metal precursor is Nand a number of the pulses of the second metal precursor is M, where Nand M may be any positive integers.

FIG. 6 provides an exemplary ternary gallium oxide thin film formed overa substrate by the thermal ALD process illustrated in FIG. 5 . Thethickness of the ternary gallium oxide thin film is dependent on thenumber of ALD growth cycles conducted. The substrate may be formed ofsilicon.

FIGS. 7A and 7B illustrate experimental QCM observations for ternarygallium oxide film growth on a silicon substrate. The ternary galliumoxide film grows by the ALD process by using Ga(amd)₃ as the first metalprecursor, TMA as the second metal precursor, and water as an oxygensource. FIG. 7A shows a film growth of the ternary gallium aluminumoxide film with a 1:1 Ga(amd)₃:TMA pulse ratio, where the ternarygallium aluminum oxide film grows about 10 Å thickness in about 600seconds. FIG. 7B shows another film growth of the ternary galliumaluminum oxide film with a 1:2 Ga(amd)₃:TMA pulse ratio, where theternary gallium aluminum oxide film grows about 20 Å thickness in about800 seconds. The metal precursor Ga(amd)₃ and the TMA precursor showsustained bulk growth of ternary gallium oxide film with water.

Herein, the pulse ratio of Ga(amd)₃:TMA is only illustrated as 1:1 and1:2. However, other pulse ratios of Ga(amd)₃:TMA can be applied withinone ALD growth cycle to achieve different concentration ratio of galliumversus aluminum in the resulting ternary gallium oxide thin film. Ingeneral, there is no limit for the pulse ratio of the first metalprecursor and the second metal precursor applied in one ALD growthcycle. With different pulse ratio of the first metal precursor and thesecond metal precursor, the concentration ratio of gallium versus thesecond metal element in the resulting ternary gallium oxide thin film, afinal thickness of the resulting ternary gallium oxide thin film, and/orthe duration to form the resulting ternary gallium oxide thin film maybe different.

It is contemplated that any of the foregoing aspects, and/or variousseparate aspects and features as described herein, may be combined foradditional advantage. Any of the various embodiments as disclosed hereinmay be combined with one or more other disclosed embodiments unlessindicated to the contrary herein.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A method of a thermal atomic layer deposition(ALD) process of depositing a ternary gallium oxide thin film, whichincludes gallium, a metal element other than gallium, and oxygen, themethod comprising: providing a reactive surface; conducting one or moreALD growth cycles, wherein each of the one or more ALD growth cyclescomprises one or more first ALD sub-cycles and one or more second ALDsub-cycles, wherein: conducting each of the one or more first ALDsub-cycles comprises: applying a pulse of a first metal precursor, whichis a gallium compound comprising one or more of an alkyl ligand, anamido ligand, an amidinato ligand, an alkenyl ligand, and a guanidinatoligand; and applying a pulse of an oxygen source after applying thepulse of the first metal precursor; and conducting each of the one ormore second ALD sub-cycles comprises: applying a pulse of a second metalprecursor, which includes the metal element other than gallium; andapplying a pulse of an oxygen source after applying the pulse of thesecond metal precursor.
 2. The method of claim 1 wherein: the oxygensource in each of the one or more first ALD sub-cycles is water; and theoxygen source in each of the one or more second ALD sub-cycles is water.3. The method of claim 1 further comprising repeating the ALD growthcycle.
 4. The method of claim 1 wherein conducting each of the one ormore ALD growth cycles comprises conducting one first ALD sub-cycle andconducting one second ALD sub-cycle in series.
 5. The method of claim 4wherein the first ALD sub-cycle is conducted before the second ALDsub-cycle within one ALD growth cycle.
 6. The method of claim 4 whereinthe first ALD sub-cycle is conducted after the second ALD sub-cyclewithin one ALD growth cycle.
 7. The method of claim 4 further comprisingrepeating the ALD growth cycle.
 8. The method of claim 1 whereinconducting each of the one or more ALD growth cycles comprisesconducting one first ALD sub-cycle and conducting two sequential secondALD sub-cycles.
 9. The method of claim 8 wherein the first ALD sub-cycleis followed by the two sequential second ALD sub-cycles within one ALDgrowth cycle.
 10. The method of claim 9 further comprising repeating theALD growth cycle.
 11. The method of claim 2, wherein conducting each ofthe one or more first ALD sub-cycles further comprises one purge stepbetween applying the pulse of the first metal precursor and applying thepulse of water, and another purge step after applying the pulse ofwater.
 12. The method of claim 2, wherein conducting each of the one ormore second ALD sub-cycles further comprises one purge step betweenapplying the pulse of the second metal precursor and applying the pulseof water, and another purge step after applying the pulse of water. 13.The method of claim 1 wherein the first metal precursor has a formula ofGaL1(L2)₂, wherein: Ga is a central gallium atom, and L1 and L2 areligands surrounding the central gallium atom; and each of L1 and L2 isan alkyl ligand, an amido ligand, an amidinato ligand, an alkenylligand, or a guanidinato ligand.
 14. The method of claim 13 wherein L1and L2 are a same ligand.
 15. The method of claim 13 wherein L1 and L2are different ligands.
 16. The method of claim 13 wherein each of L1 andL2 is selected from one of a N,N′-diisopropylacetamidinato-group (-amd),a N,N′-diisopropylformamidinato-group (-famd), a methyl group (-Me), aN-butyl group (-nBu), a vinyl group (-vinyl), a dimethylamido-group(-NMe₂), and a N,N′-diisopropyl-N-dimethyl-guanidinato-group (-guan).17. The method of claim 16 wherein the first metal precursor is one of agroup consisting of Ga(amd)₃, [Ga(famd)₃]₂, Ga(amd)₂(Me), Ga(amd)(Me)₂,Ga(amd)(nBu)₂, Ga(amd)(vinyl)₂, Ga(amd)(NMe₂)₂, Ga(guan)(NMe₂)₂, and[Ga(NMe₂)₃]₂.
 18. The method of claim 1 wherein the second metalprecursor is an organic aluminum precursor.
 19. The method of claim 1wherein the first metal precursor is Ga(amd)₃, the second metalprecursor is Trimethylaluminium (TMA), and the ternary metal oxide thinfilm is formed of gallium aluminum oxide (GaxAl1-x)₂O₃, wherein 0<x<1.20. The method of claim 1 wherein a concentration ratio of galliumversus the metal element in the resulting ternary gallium oxide thinfilm from the thermal ALD process is dependent on a pulse ratio betweenpulses of the first metal precursor and pulses of the second metalprecursor within one ALD growth cycle.
 21. The method of claim 21wherein the concentration ratio of gallium versus the metal element inthe resulting ternary gallium oxide thin film is further dependent onsub-cycle order in one ALD growth cycle, pulsing time of each pulse ofthe first metal precursor, and pulsing time of each pulse of the secondmetal precursor.
 22. The method of claim 1 wherein, in one ALD growthcycle, a number of the pulses of the first metal precursor is N, and anumber of the pulses of the second metal precursor is M, wherein N and Mare positive integers.